The metabolism of 20-carbon polyunsaturated fatty acids, particularly arachidonic acid, by prostaglandin H synthase results in a wide range of oxidized products with potent biological activities. Among these metabolites, a group of compounds called prostaglandins has drawn the attention of both scientists and medical practitioners. Prostaglandins can be manufactured from polyunsaturated fatty acids with the help of enzymes from mammals. The yield of the desired prostaglandin can be increased by means of various activators, enzyme recycling, immobilised enzymes or semibatch processes with either continuous or stepwise addition of the substrate.